This invention relates to the fabrication of oxide layers from Al-containing Group III-V compound layers.
The possibility of extremely high speed integrated circuits capable of handing data at gigabit rates had led many workers to investigate the substitution of GaAs for Si in the fabrication of field effect transistors (FETs). Two promising GaAs FET structures for medium scale integration of digital circuits are the MESFET (metal semiconductor FET) and the JFFET (junction FET). In addition, encouraging results have been recently obtained with GaAs IGFETs (insulated gate FETs), but their performance still does not rival that of Si IGFETs. Nevertheless, because an IGFET, in contrast to a MESFET or JFET, is operative with either polarity voltage and has a high input impedance, there is strong motivation for continuing research and development to improve the performance of GaAs IGFETs.
One factor detracting from their performance has been the inability to form gate insulators with adequate dielectric and interface properties on GaAs. Although silicon oxynitrides and anodic native oxides can be formed on GaAs, the native oxides tend to be unstable or of insufficient dielectric stength and both exhibit a significant amount of dispersion and hysteresis in capacitance-voltage measurements. Dispersion and hysteresis are caused by interface states between the dielectric and semiconductor, a problem addressed by H. C. Casey, Jr. et al who proposed (Applied Physics Letters, Vol. 32, p. 678, May 1978) the use of semi-insulating, epitaxial AlGaAs doped with a deep level impurity such as oxygen instead of an oxide layer for the gate dielectric. While their work demonstrated the elimination of hysteresis and dispersion, there still remains some question about the dielectric strength of the semi-insulating AlGaAs and the ability to achieve carrier inversion in the semiconductor.